1. Field of the Invention
This invention relates to a cis-1,4-substituted 2-butene derivative useful for liquid crystal materials. More particularly, it relates to a liquid crystal compound containing a 2Z-butenyl group inside its molecule and a liquid crystal composition containing the same.
2. Description of the Related Art
Display elements making use of liquid crystals have been broadly utilized for clocks, electric computers, etc. These liquid crystal display elements utilize the optical anisotropy and dielectric anisotropy of liquid crystal substances. Liquid crystal phases include a nematic liquid crystal phase, a smectic liquid crystal phase and a cholesteric liquid crystal phase. Among these phases, display elements utilizing nematic liquid crystal have been most broadly practically used. Further, display modes applied to the liquid crystal display includes TN (twisted nematic) mode, DS (dynamic scattering) mode, guest-host mode, DAP mode, etc. Many liquid crystalline compounds including those at a studying stage have been known, but at present, there is no single substance which is sealed in a display element and used. This is because while liquid crystal substances for display elements are preferred to be those which exhibit liquid crystal phase within a temperature range as broad as possible around a room temperature at which they are most often used as display elements in the natural fields, and further they should be sufficiently stable to environmental factors and have sufficient physical properties for driving the display element, a single substance satisfying these conditions has not yet been found. Thus, at present, liquid crystal compositions having such characteristics have been prepared by mixing several kinds of liquid crystal materials or further mixing non-liquid crystalline compounds therewith. Further, these liquid crystal compositions are required to be stable to moisture, light, heat, air, etc. usually present under the environment where they are used. Further, the compositions are required to be stable to electric field and electromagnetic irradiation, and further the liquid crystal compounds to be mixed are required to be chemically stable to one another under the environment where they are used. Further, the values of various physical properties such as optical anisotropy value, dielectric anisotropy value, conductance value, etc. are required to be suitable depending on a display mode and a shape of element. In particular, the importance of a substance having a low optical anisotropy value as a material for liquid crystal display element of thin film transistor (TFT) mode is increasing. In order to meet such requirements, single liquid crystal compounds having various characteristics have been developed, and as a compound for improving the values of viscosity and optical anisotropy, compounds having flexible cross linking portions between molecules have been found. For example, the following compound A having a carbon chain in the central portion of a molecule is disclosed in Japanese patent application laid-open No. Sho 61-215336. Furthermore, West German patent application laid-open No. 4027840 discloses the following compounds B having a chain of four carbon atoms as a central group in order to make the molecular structure more flexible. Japanese patent application laid-open No. Hei 3-66632 also discloses the following compound C. Further, as to a liquid crystalline compound having a chain of four carbon atoms including an unsaturated bond, no examples have been known except the following compound D disclosed as a synthesized intermediate compound in Japanese patent application laidopen No. Hei 3-66632. However, such substituted stylene compounds as the compound D are thermally unstable. Thus, there have not been known any liquid crystal material having a chain of four carbon atoms and unsaturated bond(s), and usable in the ordinal environment.
Compound A (Japanese patent application laid-open No. Sho 59-225129): ##STR2##
Compound B (West German patent application laid-open No. 4027840. A1): ##STR3##
Compound C (Japanese patent application laid-open No. Hei 3-66632): ##STR4##
Compound D (Japanese patent application laid-open No. Hei 3-66632): ##STR5##
The present inventors have made extensive research in order to solve the above-mentioned problems, and as a result, have found a compound having a novel structure and having improved characteristics as compared with generally known liquid crystal compounds, and have completed the present invention, which compound is expressed by the following formula (I): ##STR6## wherein R.sup.1 represents an alkyl group of 1 to 10 carbon atoms; n represents 1 or 2; X represents a hydrogen atom, an alkyl group, a halogen atom, a cyano group, an alkoxy group, a methyl group substituted by 1 to 3 halogen atoms, or a trihaloalkoxy group; Y and Y' each independently represents a hydrogen atom or a halogen atom.
It has been possible to apply an unsaturated group to an intermediate group adjacent to an aromatic ring to obtain a thermally stable compound resistant to use in the ordinal environment by separating the unsaturated group by one carbon atom from an aromatic ring. Thus, the compound of the present invention has a moderately rigid and free structure as compared with known compounds to be easily oriented within a liquid crystal phase, and has a relatively high elastic constant ratio. Further, the compound of the present invention has characteristics of forming a liquid crystal phase within a broad temperature range, although it has a high flexible 1-butenyl group within a molecule, and having a moderate optical anisotropy value and a very low viscosity. Further, the compound of the present invention is stable chemically and thermally, and not degraded under conditions of electromagnetic radiation, impression of electric voltage, etc. In addition, in the case where the compound of the present invention is used as a component of a liquid crystal composition, it has a superior compatibility with other liquid crystal materials to make it possible to compose a novel liquid crystal display element having useful characteristics. Further, the compound of the present invention can vary its characteristics by modifying its ring structures and the substituents on the rings thereof. Among the compounds of the present invention, preferable ones are exemplified as follows.
A compound of the formula (I) wherein n=1, X=C.sub.2 H.sub.5, Y=H, Y'=H: ##STR7##
A compound of the formula (I) wherein n=1, X=C.sub.3 H.sub.7, Y=H, Y'=H: ##STR8##
A compound of the formula (I) wherein n=1, X=C.sub.5 H.sub.11, Y=H, Y'=H: ##STR9##
A compound of the formula (I) wherein n=1, X=F, Y=H, Y'=H: ##STR10##
A compound of the formula (I) wherein n=1, X=F, Y=F, Y'=H: ##STR11##
A compound of the formula (I) wherein n=1, X=F, Y=F, Y'=F: ##STR12##
A compound of the formula (I) wherein n=1, X=CN, Y=H, Y'=H: ##STR13##
A compound of the formula (I) wherein n=1, X=CN, Y=F, Y'=H: ##STR14##
A compound of the formula (I) wherein n=1, X=CF.sub.3, Y=H, Y'=H: ##STR15##
A compound of the formula (I) wherein n=1, X=OCF.sub.3, Y=H, Y'=H: ##STR16##
A compound of the formula (I) wherein n=2, X=C.sub.2 H.sub.5, Y=H, Y'=H: ##STR17##
A compound of the formula (I) wherein n=2, X=C.sub.3 H.sub.7, Y=H, Y'=H: ##STR18##
A compound of the formula (I) wherein n=2, X=C.sub.5 H.sub.11, Y=H, Y'=H: ##STR19##
A compound of the formula (I) wherein n=2, X=F, Y=H, Y'=H: ##STR20##
A compound of the formula (I) wherein n=2, X=F, Y=F, Y'=H: ##STR21##
A compound of the formula (I) wherein n=2, X=F, Y=F, Y'=F: ##STR22##
A compound of the formula (I) wherein n=2, X=CN, Y=H, Y'=H: ##STR23##
A compound of the formula (I) wherein n=2, X=CN, Y=F, Y'=H: ##STR24##
A compound of the formula (I) wherein n=2, X=CF.sub.3, Y=H, Y'=H: ##STR25##
A compound of the formula (I) wherein n=2, X=OCF.sub.3, Y=H, Y'=H: ##STR26##
A compound of the formula (I) wherein n=2, X=OCF.sub.3, Y=F, Y'=H: ##STR27##
A compound of the formula (I) wherein n=2, X=OCF.sub.3, Y=F, Y'=F: ##STR28##
A compound of the formula (I) wherein n=2, X=OCF.sub.3, Y=F, Y'=H: ##STR29##
A compound of the formula (I) wherein n=2, X=OCF.sub.3, Y=F, Y'=F: ##STR30##
Among these compounds, those of I-g, I-h, I-q and I-r having a cyano group afford a large dipole moment, and those of I-i and I-s having a trifluoromethyl group reduce viscosity and afford a large polarizability, and thus, they are preferred. Further, among the compounds of the present invention, those having three six-membered rings within the molecule, i.e. the so-called three-rings compounds are preferable, since they can establish a liquid crystal temperature range in the vicinity of a room temperature, and broaden the temperature range.
Among the compounds of the present invention, those expressed by the formula (I) wherein R.sup.1 represents an alkyl group of 2 to 5 carbons are preferred in that they can broaden the liquid crystal range.
The liquid crystal composition provided by the present invention is preferred to be a liquid crystal dielectric material comprising a component (A) containing at least one of compounds expressed by the formula (I), and besides, a component (B) containing at least one of compounds of a high dielectric anisotropy of preferably .DELTA..epsilon..gtoreq.5, a component (C) containing at least one of a low dielectric anisotropy of preferably .vertline..DELTA..epsilon..vertline.&lt;5 and a component (D) containing at least one of compounds having a clear point exceeding 80.degree. C., and if necessary, another component (E).
Preferably compounds for the component (B) are shown below. ##STR31##
In the above compounds, R represents an alkyl group or alkenyl group of 1 to 10 carbon atoms, and one carbon atom or two carbon atoms not adjacent to each other in the group may be replaced by oxygen atom(s).
Particularly preferable compounds for the component (C) are shown below. ##STR32##
In these compounds, R and R' represent an alkyl group or alkenyl group of 1 to 10 carbon atoms, and one carbon atom or two carbon atoms not adjacent to each other in the group may be replaced by oxygen atom(s).
Particularly preferable compounds for the component (D) are shown below. ##STR33##
In the above compounds, R and R' represent an alkyl group or alkenyl group of 1 to 10 carbon atoms, and one carbon atom or two carbon atoms not adjacent to each other in the group may be replaced by oxygen atom(s).
Particularly preferable compounds for the component (E) are shown below. ##STR34##
In the above compounds, R represents an alkyl group or alkenyl group of 1 to 10 carbon atoms, and one carbon atom or two carbon atoms not adjacent to each other in the group may be replaced by oxygen atom(s).
The composition according to the present invention contains at least one compound expressed by the formula (I) preferably in a proportion of 0.1 to 40% by weight, from the aspect of affording a liquid crystal having superior characteristics.